This invention relates to pneumatic tires, and more particularly, to an improved tire for use on ice or snow covered roadways.
As the tread portion of a pneumatic tire travels through the footprint with the roadway, many different forces are experienced. Under normal dry road conditions, the principal lateral force experienced by the tread portion of the tire is the longitudinal force parallel to the direction of travel of the tire. The lateral force experienced by the tread portion under dry road conditions is generally so small when compared to the longitudinal force to be of any major consequence. However, ice and snow covered roadways present a substantially reduced coefficient of friction between themselves and the tread portion of the tire. As a result, lateral stability of the tread portion of the tire is of increased importance.
To obtain the increased lateral stability necessary to operate a motor vehicle on an ice or snow covered roadway, various non-skid devices using hardened metals have been devised. These include tire chains and studs inserted into the tread portion of a tire. The tire chains are inconvenient since one must stop the vehicle and install the chains on the driven wheels when necessary. This is time consuming and must be done in freezing weather conditions beside the roadway. In addition, the use of chains forces the driver to proceed at a slower speed than he might otherwise be able to travel due to the uncomfortable ride chain equipped tires provide. Another undesirable feature of tire chains is their potential to damage the body of the vehicle on which they are mounted if they break while traveling.
Tire chain or stud equipped tires when used on roadway surfaces that are clear of ice and snow present several undesirable side-effects. Not only are they noisier than tires not so equipped, they also cause physical damage to the surface of the roadway when the hardened metal strikes it. Small pieces of the roadway are broken free by such impact which not only increase the maintenance costs of the roadway but also presents dust pollution which is an increasingly serious social and environmental problem.
To overcome these problems, it is desirable to have a tire with a tread design which offers a non-skid footprint pattern which is resistant to forces in all directions without the use of hardened metal devices. The present invention provides such a tread design.
In accordance with the illustrated embodiments, the present invention provides a pneumatic ice and snow tire for a vehicle having a tread that includes a roadway bearing surface having defined therein a plurality of spaced-apart means for establishing suction between the tread and ice and snow on a roadway.